Agricultural aircraft are generally used in areas which are inaccessible to ready supplies of spare parts. This necessitates that the operator of the aircraft maintain an inventory of the critical spare parts which he may need in the field. In the past the filter systems for a gas turbine engine utilized inertial separators which are both complicated and expensive and necessarily would tie up a significant amount of funds (approximately $3,000 per filter) if the operator were to maintain an inventory of spare filters for his aircraft engine. In addition, this type of aircraft is used in extremely dirty environments. Huge quantities of flying insects take flight into the path of the aircraft which is flying low over crops to dust or spray insecticides. The inertial separator filter systems generally are only 87% to 92% efficient and, therefore, may allow significant contamination of the inlet airflow to the gas turbine engine. Also, the inertial separators are generally used in association with ram recovery scoops which obstruct the aerodynamic contour of the aircraft to provide a higher pressure inlet airflow to improve performance. This creates additional filter problems in that it facilitates entry of insects and other contaminants into the inlet airflow.
This invention allows the operator to use readily available automotive barrier filters which are significantly less expensive than the inertial separator systems. These filters are more readily available and an inventory of spares can be maintained with a minimum of investment. The filter system of this invention is almost 99.5% efficient and, therefore, results in a much less contaminated inlet airflow for the gas turbine engine.